There is an increasing concern to reduce the consumption of resources, both at a domestic level in residential buildings, and at a commercial level in offices, shops, factories and so forth. The reasons for this are both to save costs and also because of concerns for the environment, such as the conservation of scarce resources, for example water in regions where rainfall is low, to reduce CO2 emissions, and to conserve finite resources such as coal, gas and oil.
Conventionally, consumers receive bills from utility companies that may indicate the quantity of the utility used since the last bill, for example monthly or quarterly, based on periodic meter readings or even based on estimates of consumption since the last meter reading. For example, in the case of electricity supply, the information is presented to the consumer in terms of the number of kilowatt hours of electrical energy that has been used, which is meaningless to many people, and gives very little idea about how they are actually using the energy and where they can cut back. Studies have shown that the effect of providing consumers with real-time detailed information about the energy they are using is that their consumption reduces by up to 20%. In order to provide this information, it is necessary to identify where the energy drawn from this supply is ending up, i.e. which appliances are being used, how much and when. It is a problem to provide this information.
Devices are known which can be plugged into a conventional electricity outlet socket that can monitor the energy consumption by a particular appliance (an appliance will also be referred to herein more generally as an electrical load or simply a ‘load’) plugged into that socket. However, this information is inconvenient to obtain, and for fully monitoring the consumption at a particular site, such as a house, a separate metering device would have to be plugged into every socket to monitor every appliance, and it is generally not possible to connect such metering devices to permanently-wired appliances, such as cookers, which are typically some of the largest consumers of energy. Lighting also accounts for a significant amount of energy usage in domestic residences, for example on average 20% of the typical electricity bill in the UK is spent on lighting. Much lighting is provided in permanently wired light fittings, so a non-intrusive monitoring system is desired in this case.
Non-Intrusive Appliance Load Monitoring (NIALM) systems are known which attempt to detect signatures in the supply of the utility that are characteristic of particular appliances, including, for example, monitoring to detect events when appliances are switched on or off. For example, U.S. Pat. No. 4,858,141 (Hart et al.) discloses monitoring the voltage and current of the electricity supply to a residence to try to determine which appliances are running at any particular time and to determine the energy consumed by each.
However, distinguishing between certain types of load can be difficult in some cases.
For example, dimming devices (also called dimmer switches) are often fitted to lighting systems to allow variable control of the lighting level. These dimmer switches present a significant challenge to electricity usage monitoring systems because they transform a load that is nominally resistive and of fixed power, to a continuously variable power load, which additionally has a variable reactive power dependent on the level of dimming. There is a problem in providing a reliable way of distinguishing such loads and of measuring the power consumed by this class of device.
U.S. Pat. No. 5,483,153 (Leeb and Kirtley) discloses a ‘transient event detector’ that attempts to match various transient ‘basis shapes’ with an observed electrical waveform to assist with the appliance classification and identification process. However, there is the problem of distinguishing between appliances that have very similar characteristics with regard to consumption of electricity, for example appliances that present substantially the same electrical load. A particular problem is with heating appliances which generally have a resistive heating element which presents a purely resistive load, making it difficult to distinguish between say a toaster and a kettle. Therefore it may not be possible to separately totalize the power consumed by two 1200 W resistive appliances e.g. a toaster and a quartz space heater.
As another example, Yamagami et al., “Non-Intrusive Submetering of Residential Gas Appliances”, Proceedings of the American Council for an Energy Efficient Economy (ACEEE) Summer Study, Pacific Grove, Calif., Aug. 25-31, 1996, 1.265-1.273, discloses accurately metering gas consumption in individual homes, then analysing the data to estimate use by particular types of gas appliance, such as cooker, stove, water heater etc. However, there is the problem of distinguishing between appliances which have very similar characteristics with regard to consumption of the same utility, for example appliances which present substantially the same electrical load.
The present invention aims to alleviate, at least partially, one or more of the above problems.